Changes in cannabis laws overseas have not been found to have a significant impact on rates of adult use.
“There is little evidence that decriminalisation of (cannabis) use necessarily leads to a substantial increase in cannabis use.” – The US National Academy of Sciences
In short: legal access does not lead to increased use.
When it comes to use by young people, several recent reports have found that in the majority of US states that have approved medical cannabis, use among teenagers has actually decreased.
Experts say this is due to a diminished “forbidden fruit” effect and decreased access to cannabis as it moves from the unregulated streets – where there are no age requirements – to inside licensed dispensaries, where you need to be 21 to purchase cannabis.